Swim fins have long been used for skin diving, scuba diving, and other recreational and nonrecreational uses in order to create greater propulsive forces than can be accomplished by the foot alone. A swim fin generally consists of a portion for securing the fin to the users foot as well as a web or blade that is supported to extend from the front part of the foot for assisting in propulsion.
The stiffness of the blade or web of swim fins relates to the energy needed for proper operation of the blade. The more flexible the blade, the less energy and strength required for that particular pair of fins. However, the more flexible the blade, the slower the speed that is achievable. For that reason, beginner swimmers or swimmers having limited physical strength should ordinarily choose swim fins with more flexible blades. On the other hand, as the swimmer's strength increases, swim fins with stiffer blades should be used to achieve maximum speed and efficiency.
In addition, swimmers using swim fins for prolonged time periods tire. Under those circumstances, it is desirable to use swim fins with greater flexibility as the use of the fins continue over a prolonged time period.
Heretofore, the only solution commonly available to a swimmer wishing to change the stiffness of the swim fins being used is simply to substitute a swim fin with stiffer blades.
As a result, swimmers have often used swim fins that are much too stiff for them in the hope that with continued use and practice, and consequent pain and discomfort, the swimmer would be accustomed to the stiffer swim fin.
Existing swim fins conventionally include side ribs which have outerwalls that are either convex or lie in a plane perpendicular to the plane of the web. These ribs may bend or collapse over the surface of the web when the fin is flexed. If so, the flexing or bending of the fin is not smooth and the efficiency of the fin is impaired.
Insofar as the applicant is aware, there have been no direct efforts to solve this problem, although there have been several designs of swim fins having reinforcing elements within the blade for a variety of purposes. Thus, for example, the applicant is aware of U.S. Pat. Nos. 4,007,506 issued Feb. 15, 1977, 3,649,979 issued Mar. 21, 1972, 3,913,158 issued Oct. 21, 1975, 4,083,071 issued Apr. 11, 1978, 3,055,025 issued Sept. 25, 1962 and 4,627,820 issued Dec. 9, 1986. While each of these patents relate to swim fins, and to various treatments of the blade or web, none of them appear to deal directly with the problem of providing a blade with adjustable or variable stiffness.